CED (Cathode Electro Deposition)

Abstract. The model of organic film growth on a cathode during electrodeposition process proposes the current density-time and film thickness-time relationships and enables the evaluation of the rate contants for the electrochemical reaction of OH– ion evolution and for the chemical reaction of organic film deposition. The dependences of film thickness and rate constants on the applied voltage, bath temperature and resin concentration in the electrodeposition bath have also been obtained. The deposition parameters have a great effect on the cathodic electrodeposition process and on the protective properties of the obtained electrodeposited coatings. From the time dependences of the pore resistance, coating capacitance and relative permittivity, obtained from impedance measurements, the effect of applied voltage, bath temperature and resin concentration on the protective properties of electrodeposited coatings has been shown. Using electrochemical impedance spectroscopy, thermogravimetric analysis, gravimetric liquid sorption experiments, differential scanning calorimetry and optical miscroscopy, the corrosion stability of epoxy coatings was investigated. A mechanism for the penetration of electrolyte through an organic coating has been suggested and the shape and dimensions of the conducting macropores have been determined. It was shown that conduction through a coating depends only on the conduction through the macropores, although the quantity of electrolyte in the micropores of the polymer net is about one order of magnitude greater than that inside the conducting macropores.

Keywords: electrodepositon, cathodic electrodeposition, epoxy coatings, corrosion protection, corrosion stability.

Introduction Electrodeposition of organic coatings has gained worldwide acceptance as a coating processforautomotive,applianceandgeneralindustrialcoatingswhichhasbeenadoptedin technology to provide the first prime coat to a variety of products. The advantages of the process are its automated character, high level of paint utilization, low level of pollution and high throwing power, i.e., the ability to coat recessed areas of complex metal shapes. Cathodic electrodeposition has assumed major commercial significance due to the avoidance of electrochemical dissolution of metal, the impossibility of electrochemical oxidation of the resin at the substrate and the better corrosion protection. Fundamental aspects of electrodeposition process have been reported by Beck.1–6The theory which explains organic film formation and the mechanism of film growth has been developed through many investigations, as reported by Pierce and coworkers.7,8 The similarity of the growth kinetics of organic coatings and oxide films has been demonstrated.9,10